Highly successful British Security Service MI5 break-in (Black Bag Job) operation against the Communist Party of Great Britain in 1955. A telephone tap on a Mayfair apartment in London, where the party membership files were known to be kept, revealed when the apartment would be empty and a latchkey left under the doormat.
MI5 operatives quickly went to the apartment and made a wax impression of the key. Then, when the occupants were away for the weekend, operatives entered the apartment, picked the locks on file cabinets, carted away their contents to be photographed, and then carefully set them back in place.
The files -- numbering 55,000 items -- revealed the complete membership of the Party, recruitment techniques, and other details.
